Then, the saber-rattling grew louder: Iran drew a line in the Persian Gulf and warned a U.S. aircraft carrier not to return.

Mounting tensions in the gulf usually prompt frantic diplomatic efforts to calm the waters. Not this time. Iran's shrill pronouncements are powerful evidence that Tehran feels the economic squeeze of U.S. and EU sanctions, aimed at halting Iran's rogue nuclear program.

More evidence: Iran's currency has plunged by 40 percent against the dollar in a month.

The mullahs are spooked — for good reason. The EU has “agreed in principle” to ban Iranian imports, Reuters reported Wednesday.

That embargo would deal a devastating economic blow to Tehran. EU imports account for about 18 percent of Iran's oil export business.

Oil expert Robert McNally of the Rapidan Group calls the embargo strategy “reaching for Iran's oil jugular.”

It's a bold and brilliant move. The United States, which does not import Iranian oil, should strongly back the EU action.

About that Iranian threat to barricade the Strait of Hormuz: It's hollow. Iran's previous attempts to restrict traffic in the strait failed miserably in the 1980s.

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Still, even the threat of a pinched oil supply is enough to send prices and insurance rates spiking. And even if Iran didn't block the strait, its forces could disrupt oil supplies elsewhere.

So, yes, an EU embargo of Iranian oil could spur economic havoc.

But that embargo and a freeze of Tehran's central bank assets by the United States and its allies are still the best diplomatic options on the table to thwart Iran's nuclear ambitions. Taking the risk of economic upheaval now cuts the odds of a military strike against Tehran's nuclear program by a jittery Israel.

For years, the mullahs have brushed off sanctions and bulled ahead with a nuclear program that could unleash an atomic arms race.

In November, the International Atomic Energy Agency provided compelling evidence of an Iranian nuclear weapons program.

Iran's threats unsettle many U.S. allies in the region. Key U.S. allies, including Saudi Arabia, Iraq and the United Arab Emirates, depend on the Strait of Hormuz to transport their oil.

But imagine something else. Imagine that Iran has the bomb. Imagine it has nuclear weapons to back up its bluster and cement the tyrannical mullahs in power. Imagine how different the diplomatic exchanges would be right now.